Masonry Magazine October 1994 Page. 32
Masonry Construction in Variable Weather
Favorable weather for the construction of the exterior wythe is sensible. The type of joint reinforcement and masonry tie used should consider the fact that three or four wire joint reinforcement should be replaced with two wire reinforcement in the inner wythe and adjustable masonry ties and a single or double wire joint reinforcement be included in the exterior wythe. This procedure avoids bending joint reinforcement upward during laying the course immediately below the reinforcement.
Several systems are available for cold weather enclosure of scaffolding. Single stage scaffolding can be effectively sealed at its outer perimeter using reinforced or non-reinforced plastic membrane. The enclosure thus becomes a windbreak and a containment for auxiliary heat. Swinging stage and climbing scaffolding allows concentrating the work area and windbreak or heated enclosure to the work location. Shades or mesh attached to a climbing scaffold platform are equally effective. Avoidance of constructing the sunny face of the structure during the hot part of the day should be scheduled, if possible.
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Masonry construction
Regardless of climatic conditions, masonry construction should proceed being attentive to the wall design, be it a barrier wall or a cavity wall. Barrier walls must be constructed with full mortar bed and head joints and mortar or grout completely filling any air spaces between adjacent wythes. Cavity walls must be constructed so the cavity between wythes is free of mortar droppings or protrusions. Flashings must be continuous and weepholes spaced every "x" number of units. Flashings should possess end dams, be lapped with laps sealed and project outward from the face of the exterior masonry wythe.
Weather conditions should not be allowed to have an effect on the masonry construction. Cold temperature mortars will require less tempering of the masonry mortar; hot weather will require more frequent tempering. It's generally more sensible to provide an adequate working atmosphere than to be concerned with the weather effects on materials and masonry.
Protection of completed masonry
All completed masonry should be covered during work stoppages and after the masonry segment is completed. Water entering the top surface of the masonry segment will saturate the wall, cause soluble compounds to be released and show as leachates or efflorescence, and subject the wall to damage if freezing occurs. The covers should remain in good condition until allied trade covers the top surface of the masonry segment.
Weather covers for masonry segments should be selected on basis of historical weather information and weather forecast. During cold and sunny days, clear plastic sheeting allows solar radiation to penetrate the membrane and provide some heat to the masonry. Conversely and on hot and sunny days, black plastic sheeting is preferred, as black surfaces warm and cool faster than white surfaces.
Grouted masonry should receive special attention during cold weather masonry construction. Because grout is contained in the collar joint or cells of units, the wind chill (rate of cooling) effects are lessened. The high water content grouts, however, can undergo disruptive expansion if the grouted masonry is unprotected.